In Sarah Polley’s “Take This Waltz,” Michelle Williams plays Margot, a not-quite-happily married wife who strays. Her husband, Lou (Seth Rogen, in a good, uncharacteristically tamped-down performance), writes cookbooks. Her lover, Daniel (Luke Kirby), is an aspiring artist who pulls a rickshaw. It’s as contrived as it sounds.

Margot spends a lot of time in the sweltering Toronto summertime looking wan and winsome. The very odd Daniel looks he’s pulled one too many rickshaws. Lou’s upcoming book, though – it’s titled “Tastes Like Chicken” – sounds like a winner.

Polley has a sometimes graceful understanding of emotional temperate zones and Williams, when she isn’t being zombielike, is touching. But Margot comes across as such an elusive and unsympathetic twit that you wonder why we should care about her. Grade: C+ (Rated R for language, some strong sexual content and graphic nudity.)